In a known device of this type (DE-OS No. 30 19 132) the light emitter is provided as a light conductor designed as a circular ring loop and the light emerges from its entire circular circumference. The photoelectric transducer is provided as a more or less punctiform photoelectric cell which is guided along the light conductor curved to form a circle on a corresponding circular path. As only a small fraction of the total light energy conveyed by the light conductor can be absorbed at any time with this arrangement it is relatively insensitive and unsuitable for transmitting weaker signals. In addition, the light emerging at the circumference is, in practice, inhomogeneous and leads to interferences or signal distortions.